Fabry-Perot sensors have broad utility for applications which require monitoring of absolute, static displacements and small, dynamic vibrations or oscillating changes. For example, their simplicity of design allows these sensors to be embedded into industrial applications, including gas turbines, engines, pressure vessels, pipelines, buildings or other structures, in order to provide information about pressure, temperature, strain, vibration, or acceleration within the structure. Their size, durability, and fast response time make these sensors advantageous.
Fabry-Perot fiber optic sensor 5, shown in FIG. 1, is generally known in the art. A fiber optic Fabry-Perot sensor is an interferometric sensor. Light passes through optical fiber 10. The fiber 10 terminates at partially reflective surface 12a, which is itself aligned with partially reflective surface 12b. Surfaces 12a and 12b are separated by gap G, which changes due to vibrations or other movement of at least one of the surfaces 12a, 12b. Preferably, surface 12a is fixed while surface 12b is affixed to the object being monitored and may therefore move so as to change the size of the gap G. For example, surface 12b may be affixed to diaphragms, other fibers, cantilever beams or other such structures in order to monitor the aforementioned parameters.
In operation, light travels through fiber 10, and some of this light is reflected back into fiber 10 by surface 12a. Additional light is also reflected back into fiber 10 when it strikes surface 12b. The light reflected from the two surfaces (i.e., that which is transmitted back into fiber 10 via surfaces 12a and 12b) interferes to create an interference pattern, also called a modulation pattern. When the interference pattern is monitored over time for changes, these changes are indicative of changes in the length of the gap G and very small changes or oscillations may be detected with this type of sensor 5.
Such Fabry-Perot sensors must be used in conjunction with detection and processing equipment in order to provide quantitative feedback concerning changes in gap G over a given period of time. Notably, these arrangements provide for absolute or static measurements as well as relative or dynamic measurements of the oscillations or vibrations reflected by changes in the length of the gap G. The present invention contemplates inter alia an improved absolute static sensing and an improved relative dynamic sensing system and method, which incorporates a Fabry-Perot sensor in conjunction with enhanced detection and processing capabilities to improve the sensitivity, dynamic range, frequency response, cost, and operation of the system.